Circuit interrupter



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Jun 30 1953 F1dJly22 1950 Fig.3.

` WITNESSES:

wf/W. Zz/ uur June 30, 1953 R. E. FRINK Erm. 2,644,048

CIRCUIT INTERRUPTER Filed July 22, 1950 5 Sheets-Sheet 3 INVENTORSRussell E.Frink and Eugene H.Fischer.

ATTORN Patented `lune 30, 1953 UNITED STATES PATENT OFFICE CIRCUITNTERRUPTER Application `luly 22, 1950, Serial No. 175,332

(Cl. G-144) 14 claims. 1

This invention relates to circuit interrupters in general, and moreparticularly to arc extinguisheing structures therefor.

A general object oi our invention is to provide an improved arcextinguishing structure which will more erlectively interrupt thecircuit therethrough than has been attained heretofore.

e. more speciiic object is to provide lan im proved spaced plate type oiarc extinguishn structure for circuit interrupters or" the air brea.;type, in which improved plate coniiguration utilized to more readilyassist arc extinction at an early current zero.

A further object is to provide an improved plate material for circuitinterrupters oi the ioregoi type which will have improved electricalchanl acteristics at relatively high temperatures.

A more specic object is to provide an improved refractory 'type spacedplate arc extinguislfier ol" the type utilizing slotted plates in whichlongitudinally extending grooves, substantially paralm lel to thedirection of the slots, are utilized to prevent reignition of theextinguished arc after a current zero.

Another object is to provide an improved chute in which the arc is madeto assume a serpentine or sinuous path as it moves outwardly through thechute in which longitudinally extend-s ing grooves are provided to forma lengthened creepage path in parallel with the arc to preventreignition of the extinguished varc alter a current Zero.

It is still a further object of our invention to provide an improvedrefractory material for use in an arc chute against which the arc ismoved, the improved electrical characteristics of which will morequickly bring about arc extinction.

A further more speciiic object is to provide a slotted spaced plate typeof are extinguisher in which the plates are formed of a material having"improved electrical characteristics.

Further objects and advantages will readily become apparent upon readingthe following specification, taken in conjunction with the drawn ings,in which Figure l is a side elevational view, partially in verticalsection, ci a circuit interruptor embodyw tact it.

Fig. 5 is a vertical sectional view taken along the line V-V of Fig. 4showing only the arc chute sub-assembly, and

Fig. 6 is an enlarged plan view in section tal-:en along the line VI-VIof Fig. 5 through one of the fins or projections extending outwardlyfrom one wall of the arc chute of Fig.

Referring to the drawings, and more particularly to Fig. 1 thereof, thereference numeral i designates a circuit interruptor of the air breaktype mounted upon a suitable panel structure 2. Briefly, the circuitinterruptor l comprises a blowout coil il, a U-shaped magnetic circuitil; Contact structure t separable to establish an arc and an arcextinguishing structure for quickly elicot-n ing the interruption of theestablished arc.

The contact structure 5 comprises a'terrninal stud l' surrounded by abushing il of a suitable insulating material. The terminal stud ssupports a stationary contact plate il, the latter in turn supporting amain contact lll, a secondary contact il and a relatively stationaryarcing contact it. Another terminal stud, not shown, has pivotallymounted thereon a movable Contact arm i3 carry ing a movable bridgingcontact it, a movable secondary Contact l5 and a movable arcing con-=Also electrically connected to this second terminal stud, not shown, isa main contact il'.

During the opening operation, pivotal clockwise opening rotative motionof the Contact arm i3 takes place caused by the actuation of a suitablemechanism, which forms no part of our invention. The bridging contact itrst separates from the stationary main contacts it, il to force theseries current to pass through the secondary and arcing contacts il, lliand it, i5. Continued opening rotative motion of the contact arm itsubsequently causes separation between the secondary contacts il, i5 toforce the current to pass through the arcing contacts Further openingrotative motion of the pivotally mounted movable contact arm I3 causesseparation between the arcing contacts l2, I6 to establish an arctherebetween. Because of the loop circuit formed by the two terminalstuds, and because of venting provided through the vent 23, the arc,established between the separated arcing contacts I2, I6, will bowupwardly to conu tact the arc horn lll in the manner indicated by thebroken line I9. The attachment of the lefthand arc terminal to thearcing plate or horn lll will insert into series circuit the blowoutcoil 2li which-will, upon being energized, magnetize the U-shapedmagnetic structure 4 to thereby set up a transverse magnetic field 2ibetween the pole plates 22, as shown in Fig. 2. This magnetic movablecontact arm I3 to the other terminal stud for the interrupter, notshown.

As mentioned, the 'transverse magnetic field 2l, set up between the poleplates 22 by the blow out coil 26, forces the arc 2E upwardly into thearc chute 6 which comprises a plurality of refractory spaced plates 21,which do not evolve gas upon contact with the established arc. It willbe observed that each plate 21 has a tapered slot 28 extending inwardlyfrom the lower side 29 thereof with the upper end 30 of the slot 2i! eslightly off center. That is, the center line 3i of the plate 21 passesslightly to the right of the upper end 30 or the slot 29 of the plate 21shown in Fig. 2. llhe immediately adjacent plate 21 of Fig. 2, has itsslot 28 turned 180 to that oi the slot 28 of the first plate 21 in Fig.2, so that the second plate 21 has the upper end 3c of its slot 28disposed to the right of the center line 3i of Fig. 2. The net resultis, therefore, that the upper ends 3U of the several slots 2t arestaggered *L about the center line 3l, so that when the arc 28 is at theupper ends of the slots 28 it is forced to assume a zig-zagconfiguration, as more clearly shown in Fig. 3.

For the theory pertaining to the manner oi' arc interruption in a spacedrefractory plate type of arc extinguisher, reference may be had toUnited States Patent 2,442,199, issued. May 25, 1948 to Robert C.Dickinson and Russell E. lhinli, and assigned to the assignee of theinstant applica1 tion. This Patent 2,442,199 sets forth in detail thetheory of arc extinction which is assumed to take place, and alsomentions vprior patents which forni a background for this type of arcinterrupu tion.

It will be, observed that each of the plates 21 has provided therein aplurality of srnall slots or grooves 32 in the surface plane of theplate, on each side thereof, which extend substantially parallel to thedirection of the narrow tapered portion 39 of the slot 28, the purposefor which will be more fully described hereinafter. 1t will also beobserved that spacers 34, preferably formed of asbestos rope andcemented to the reM fractory plates 21, are utilized to space the plates21 the desired distance apart. The plates 21 and the spacers 34 arecemented together, as menn tioned, and together with the arcing hornsI8, 24 form a sub-assembly 35, which is placed downwardly within therectangular arc chute housing 35, the latter being disposed between thepole plates 22 of the blowout structure 4. After the sub-assembly 35 hasbeen placed within the arc chute jacket 36, a pair of insulating holdingstrips 31 are utilized to prevent the gas pressure from forcing thesub-assembly 35 upwardly out of the are chute jacket 36. Preferably,bolts 3S are employed to secure the holding strips 31 to the upper edgesof the arc chute jacket 3G.

The slots 28 may extend in some instances for a distance of 7 to 9inches from the lower ends 28 of the plates 21. As mentioned, the upperends 3|) of the slots 28 are alternately offset so that when the arc 26is driven up into these ,notches or slots 28, it is lengthened,restricted accalmie in cross-section and subjected to the intense deiionizing action of a powerful, magnetically-in duced gas blast. All ofthese factors directly oi' indirectly bring about deionization of thearc path, and the arc is compelled to continuously ionize freshquantities of gas. If at the time interval in the region of currentzero, the rate of de-ionization exceeds that at which the arc canproduce ionization, and all insulation paths parallel to the arc areable to withstand transient and normal restored Voltage, interruption ofthe arc 26 results.

When an interruption takes place, the gas path which immediately beforehad been a conductor, does not instantly become a good insulator. At the.instant immediately following current zero, the restored voltagetransient begins to be impressed across the space previously occupied bythe arc, and current starts to flow in the reverse direction. Theproduct of this current and the voltage across the arc chute representsenergy which is re-ionizing the gas and further heating the solidinsulation. If the rate of deionization of the gas path and the rate ofconduction of heat away from the surface of the solid insulation isgreater than the rate at which the arc is ionizing and heating, then thecurrent will be interrupted. We have found that on many successiveinterruptions, this leakage current flowed from 0.1 to 0.25 cycle afterthe point of apparent interruption, and that its current magnitude wasgreater than 0.1 ampere.

We have also discovered that the limit of interrupting ability of thecircuit breaker of the foregoing type is not the ability to build. updielectric strength rapidly in the gas space previously occupied by thearc, but rather, it is the ability to hold voltage over the parallelcreepage surfaces forrned cy the ceramic material from yw'l'ich theinsulating plates are made.

Due to the intense heat generated by arcs, even highly refractoryinsulating materials may become conducting when electrical arcs areapplied over their surfaces. Many ceramic ren fractories which arenormally goed electrical inm sulators may decompose or dissociate undering conditions whereby a portion segregates or volatilizes and theresidue becomes electrically conducting. At the instant at whichinterrup" tion taires place, the surfaces of splitter platesl have justbeen exposed to arc temperatures of, perhaps, several thousand degreescentigrade. When the dielectric strength of the adjacent to these platesstarts to build up, voltage is iin pressed across the highly heatedsurface current 'flows on the surface, generatinD heat. lf the surfacewas so hot initially, or the iin-- pressed Voltage is .so high that thisheat is genn erated more rapidly than it :is dissipate", then thesurface temperature wl rise and it will becorrie even more co 1cl andcause a failure in operation of the l seeker.

We `have found that an unexpected nient in electrical characteristicscan be obtained by making the insulating plates 21 from a ceramicrefractory composed of le 'it 85% by vwegl'it of sillimanite, which hasreally good. electrical characteristics at high temperatures as occuradjacent to electrical So-called silliinanite refractorics may becoinposed of one or more of the sillinianite group oi aluminisilicateminerals: particularly andalusite, lryanite, and sillimanite. We haveobtained particularly good results with plates rnade of andalusite` Thechemical formula for all of these minerals is Al2O3.SO2. Each of themdissociates upon heating at high temperatures to free silica andmullite, 3Al2O3.2SiO2. However, in this case, the products ofdecomposition (mullite and silica) are good insulators, even at the hightemperaturesof electrical arcs. l

As an example, the body of a series of refractory plates was preparedfrom powdered andalusite admixed with a small amount (2% to 4%) of apowdered borosilicate glass, as a fluxing agent, not execeeding 3% byweight of incidental impurities such as alkali oxides and lime, and from5% to 8% of refractory type ball clay added for bonding. This bodyshould be fired at a sufliciently high temperature, at least py`rometric cone Il, to bring about at least a partial dissociation todevelop mullite crystals which greatly improves the strength, 'thermalresistance, and spalling resistance of the plate. The plates may befired to provide any desired amount of mullite or even to theextent'that they are composed essentially of mullite and a small amountof free silica which melts at approxin mately 3300 F. This offers theadvantage that even though the outermost layers of a plate may be meltedby an arc, it will still be a high 'resist-1 ance material which will bebeneficial for the reasons set forth.

We will now describe a specific example. in forming 100 pounds of thesillimanite refracftory composition 92 parts of powdered andalusite wasadmixed with three parts of powdered borosilicate glass composed of 80%SiO2, l2% B203, 7% A1203 and the balance alkali oxides, asr a fiuxingagent and ve parts of refractory ball clay (essentially aluminumsilicate) for bonding with a small amount of water to form a plasticmass. Plates were molded from the composition and fired at 2850 F., plusor minus 50 F.

Sillimanite alone may also be used without any bonding 'clay or fluxsuch as glass or lime. ln the case of the pure material the firingtemperature is necessarily higher, above 2900" A temporary binder suchas dextrin, or polystyrene should be used to bind the particles togetherto properly mold into plates. During firing the temporary binder iscarbonized and burns out.

We have also found that improved performance can be obtained by havingthe ceramic insulating plates 2l provided with their surfaces grooved,as shown more clearly in Figs. 2 and 3. The grooves 33 in the surfaceplanes of the plates are placed at right angles to the arc, and aresufciently narrow and deep that the bottoms of the grooves are notdirectly exposed to the arc. The 'creepage path in parallel with the arois then of alternate bands of hot and cold materials, the resistivity ofthe cold bands being very high. This means that even after a heavycurrent interruption, the surface over which creepage would take place,as previously described, is. so completely broken up by these relativelycold bands that breakdown will not occur due to leakage, and fulladvantage can be taken of the dielectric recovery of the gaseous arcspace. Another advantage will be realized from a struc-i ture of platesas described, Such a structure will have a higher interrupting emcien-cywhere interrupting efficiency is defined as Max. int. voltage Arcvoltage Arc voltage is largerly due to extraction of heat .from thearc.VVV 1t isevident that we have raised the maximum Vvoltageinterrupting ability without altering the structure in such a manner asto increase the heat extracted. Lower arc voltage for a giveninterrupting voltage is an advantage inasmuch as excessive arc voltageis inclined to produce switching surges.

This feature of the groove construction is applicable to insulatingplates regardless of the material from which they are made, sillima-niterefractory being preferred, but Zircon porcelain, asbestos lumber, orany other refractory mal terial being improved by such grooving.

In a particular instance, the grooves 33 were 1%; inch deep and were 1%inch apart between their centers. The width of the bottom of the groovewas als inch, and the grooves 33 extended approximateli7 3X1 inch abovethe top of the upper end 3f) of the slot 2S, as shown more clearly inFig. 2. The grooves 33 extended approximately 1 inch to one side of theslot 28, as shown in Fig. 2, and the distance between the plates 2l wasapn proximately 1A; inch, with the plates 21 being substantially 1/4inch in thickness. The total width of the plates 2l was substantially31A? inches. The lateral distance between the upper ends of the offsetslots 30 was substantially l inch.

Figs. 4 6 illustrate a further embodiment of our invention. Thisembodiment illustrates the use of our invention in an arc chute 4l ofthe type consisting of two wall members 42, 43, each of which hasprojections or fins 44, 4E which interleave with the fins or projectionsof the opposite wall member. In other words, upon the assembling of thetwo wall members 42, 43. the arc is made to assume a serpentine orsinuous path as it moves upwardly and outwardly through arc chute 4l, asviewed in Fig. 5. It will be noted that the lower ends of the fins 44and 45 are chamfered or tapered as at 46, 41 so that the arc is made togradually assume its sinuous path as it moves upwardly along theprojections 44, 45 in its upward movement through the arc chute 4|.

Preferably a suitable transverse magnetic field set up by blowoutstructure isutilized in forcing the arc upwardly through the arc chute4|. The wall members 42, 43, together with their integrallly formedprojections or fins 44, 45 are formed of the sillimanite materialhereinbefore referred to. Also preferably, the two sides of each fin orprojection 44, 45 have formed thereupon the longitudinally extendinggrooves 48, as more clearly shown in Fig. 6.

As hereinbefore referred to, when the arc is moved upwardly through lthearc chute 4| and is made to assume a sinuous form, the longitudinallyextending grooves or irregularities 48 form a lengthened creepage pathin parallel with the arc to thereby prevent reignition of the arc aftera current Zero. As previously explained, the bottoms 48d of the grooves48 are much cooler than the top plate surface and hence the material hasbetter electrical breakdown characteristics.

Although we have shown and described specic structures and material, itis to be clearly understood that the same were merely for the purpose ofillustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the appended claims.

We claim as our invention:

l. yA circuit interrupter of the air-break type including a plurality ofclosely spaced plates of insulating material having tapered slotsprovided therein, the tapered portion of the slot in each plate beingoffset from the center line of the plate and the plates beingalternately assembled with the tapered ends of the slots to the rightand to the left of the center line to form a zigzag arc passage, meansfor establishing an arc, the arc moving within the several slots andinto the zigzag arc passage, and a plurality of longitudinally extending grooves on at least one side of each of a plurality of platesadjacent the slot therein to form upon assembling a lengthened creepagepath in parallel with the arc after it has assumed a zigzagconfiguration near the closed ends of the slots.

2. A circuit interrupter of the air-break; type including a plurality ofclosely spaced plates of insulating material having tapered slotsprovided therein, the tapered portion of the slot in each plate beingoffset from the center line of the plate and the plates beingalternately assembled with the tapered ends of the slots to the rightand to the left of the center line to form a zigzag arc passage, meansfor establishing an arc, `the arc moving within the several slots andinto the zigzag arc passage, and a plurality of longitudinally extendinggrooves on both sides of each plate adjacent the slot therein to formupon assembling a lengthened creepage path in parallel with the arcafter it has assumed a zigzag con figuration near the closed ends of theslots.

3. A circuit interrupter including a plurality of spaced plates, meanslfor establishing an arc and-moving the arc against the edges oi theplates, and the plates being composed of a sillimanite refractorycomposed oi at least 85% of a mineral composed of .Al2Oz.SiO2.

4. A circuit interrupter including means i'or establishing an arc, anarc chute having insulate ing portions aga-inst 'which the arc is moved,and the insulating portions being composed of a refractory composed ofat least 85% of at least one aluminosilicate `mineral selected from thegroup consisting of A12O3-Si0i and BAlZOaIzii).

5. A circuit interrupter of the air-break type including means forestablishing an arc, an arc chute having means at least partly ofinsulating material for causing the arc to assume a sinuous form, andsaid latter mentioned means having a plurality of grooves extendingtransversely of the arc to form a lengthened creepage path in parallelwith the arc to prevent reignition after a current zero.

6. A circuit interrupter of the air-break type including means forestablishing an arc, an arc chute including two side wall members, eachhavn ing a plurality of outwardly projecting iins, the ins of one wallmember closely interleaving with the fins of the opposing wall member,the arc moving into engagement with the nns and theren by being made toassume a sinuous form, and each of a plurality of iins having at leaston one side thereof a plurality of longitudinally extend-u ing groovesdisposed transversely of the are to form a lengthened creepage path toprevent reignition of the arc after a current zero.

'7. A circuit interrupter including means for establishing an arc, anarc chute including a pair of opposing wall members, each of which has aplurality of outwardly extending iins, the iins of one Wall memberinterleaving with the ns of the opposing wall member, the arc movinginto engagement with the hns and thereby being made to assume a sinuousform, and the fins being. `composed of. a sillimanite refractory corn- 8posed of at least oi a mineral composed oi AleOaSOz,

8. A circuit breaker of the air-break type including means forestablishing an arc, an arc chute for extinguishing the arc having platemeans at least partly of insulating material for causing the arc toassume a sinuous form, the plate means having a plurality of groovesextending transversely of the arc to form a lengthened creepage path inparallel with the arc to prevent reignition after a current zero.

9. A circuit interrupter of the air-break type including means forestablishing an arc, an arc chute for extinguishing the arc having plateportions at least partly of insulating material for causing the arc 'toassume a sinuous form, at least some of the plate portions on at leastone side thereof having a plurality of grooves extending transversely ofthe arc to form a lengthened creepage path in parallel with the arc toprevent reignition after a current zero.

l0. A circuit interrupter of the air-break type including a plurality ofclosely spaced plates of insulating material having tapered slotsprovided therein, the tapered portion of the slot in each plate beingonset from the center line of the plate and the plates being alternatelyassembled with the tapered ends of the slots to the right and to theleit of the center line to form a zigzag arc passage, means forestablishing an the arc moving within the several slots and into thezigzag arc passage, and a plurality of longitudinally extending groovesin the surface plane oi at least one side of at least some of the platesadjacent the slot therein to form upon assembling a lengthened creepagepath in parallel with the arc after it has assumed a zigzagconiiguration near the closed ends of the slots.

ll. n circuit interrupter of 'the air-break type including a pluralityof closely spaced plates of insulating material having tapered slotsprovided therein, the tapered portion of the slot in each plate beingoffset from the center line of the plate and the plates beingalternately assembled with the tapered ends of the slots to the rightand to the left of the center line to form a zigzag arc passage, meansfor establishing an arc, the arc moving within the several slots andinto the zigzag arc passage, and a plurality of longitudinally extendinggrooves on both sides of at least some of the plates in the surfaceplanes of such plates adjacent the slot therein to form upon assemblinga lengthened creepage path in parallel with the arc after it has assumeda zigzag configuration near the closed ends of the slots.

l2. A circuit interrupter of the air-break type including means forestablishing an arc, an arc chute having plate means at least partly ofinsulating material for causing the arc to assume a sinuous form, theplate means having a plurality of grooves in the surface planes of theplate means extending` transversely of the arc to forni a lengthenedcreepage path in parallel with the are to prevent reignition after acurrent zero.

13. A circuit interrupter of the air-break type including means forestablishing an arc, an arc chute having plate portions at least partlyof insulating material for causing the arc to assume a sinuous form, atleast some of the plate portions on at least one side thereof having aplurality of grooves in the surface planes of such plate portionsextending transversely of the arc to form a lengthened creepage path inparallel with the arc to prevent reignition after a current zero.

14. A circuit interrupter of the air-break type including means forestablishing an are, an arc chute including tWo side wall members eachhaving a plurality of outwardly projecting fins, the ns of one Wallmember closely interleaving with the iins of the opposing Wall member,the arc moving into engagement with the iins and thereby being made toassume a sinuous form, and at least some of the fins having at least onone side thereof a plurality of longitudinally extending grooves in thesurface planes of the fins disposed transversely of the arc to form alengthened creepage path to prevent reignition of the arc 15 lilReferences Cited in the le of this patent UNITED STATES PATENTS OTHERREFERENCES Mellor, Comprehensive Treatise on Inorganic and TheoreticalChemistry, vol. 6, page 458; Longmans, Green & Co., N. Y., 1925.

